Detailed descriptions of mobile communication networks and systems can be found in the literature, in particular in Technical Specifications published by standardisation bodies such as for example 3GPP (3rd Generation Partnership Project).
In such systems, a Mobile Station (MS) or User Equipment (UE) has access to mobile services via an Access Network (AN). The Access Network (AN) generally comprises a Radio Access Network (RAN) and a Core Network (ON).
There are different types of RANs, based on different types of Radio Access Technologies, such as for example: GSM/GPRS RAN (also called GERAN), UMTS RAN (also called UTRAN), LTE RAN (also called E-UTRAN), WLAN, WIMAX, . . . etc.
Different types of mobile services can be delivered to end users, such as in particular CS (Circuit Switched) based services, PS (Packet Switched) based services, and IP (Internet Protocol) based services such as IMS (IP Multimedia Subsystem) services. The Core Network (CN) therefore comprises different domains and subsystems such as CS domain, PS domain (also called GPRS), Evolved Packet Core (EPC), IMS subsystem.
Different examples of Access Networks formed of different RANs and CN domains and/or subsystems are illustrated in FIG. 1. The architecture for EPC is specified in particular in 3GPP TS 23.401 and recalled in FIG. 2 taken from this specification.